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Red giants to probe history of Milky WayBY DR EMILY BALDWIN
ASTRONOMY NOW

Posted: 16 December, 2008

A new project based on the Sloan Digital Sky Survey III will study more than 100,000 Milky Way red giant stars to help understand the formation history of our Galaxy.

Red giant stars are luminous, bloated stars in a late stage of evolution, and contain the chemical and dynamical fingerprints needed to understand the assembly of our Galaxy. "It's the ultimate exercise in archeology," says Steven Majewski, a University of Virginia professor of astronomy and lead scientist on the project. “Our home galaxy, the Milky Way, is a typical spiral galaxy and an important laboratory for gaining a detailed understanding of galaxies in general.”

The APOGEE project will help astronomers learn about the formation of spiral galaxies like our own Milky Way. Pictured above is spiral galaxy M81 Image: NASA/JPL-Caltech/Harvard-Smithsonian CfA.

The project has been named the Apache Point Observatory Galactic Evolution Experiment (APOGEE) and is one of four experiments of the new Sloan Digital Sky Survey III using the astronomical facilities at Apache Point Observatory in New Mexico. "APOGEE will be the first truly comprehensive study of the chemistry of Milky Way stars. With APOGEE, we will gain enormous insight to the processes that make stars and that drive the formation and evolution of galaxies," says Majewski.

Infrared cameras and spectrographs will be used to peer through the dense clouds of interstellar dust that usually obscures the central regions of the Milky Way from visible light observations, and will take detailed measurements of the chemistry, motions and distances of the red giants. University of Virginia astronomer Michael Skrutskie is leading the team in the design and construction of a unique instrument that will provide unprecedented information about the Milky Way's stars. His highly specialized spectrograph will be connected to a 2.5 metre telescope at Apache Point, allowing for the detailed and simultaneous observation of 300 stars. Thousands of red giants will be observed per clear night over a period of three years. "Currently, being able to observe 10 red giants per night at APOGEE's level of detail would be considered good," says Majewski.

The team will be using the Two Micron All Sky Survey (2MASS) – a major project that surveyed the entire sky in the infrared and provided a database of more than a billion stars and galaxies – to probe 100,000 red giants using Skrutskie’s spectrograph. "APOGEE will inevitably create a lasting legacy of discovery," says University of Virginia astronomy department chairman John Hawley.

Other projects of the Sloan-III survey, carried out by teams of astronomers from an international collaboration of universities and research organisations, will attempt to detect the effects of dark energy; map the stars of the Milky Way halo, and search for evidence of planets orbiting a sampling of 11,000 nearby stars. The preceding Sloan-I and Sloan-II surveys have been widely regarded as the highest impact astronomical projects of their time, and Sloan-III is slated to be just as successful.

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